1. Field of the Invention
The present invention relates to an image forming apparatus that forms a toner image on an image carrier, transfers the toner image to a long recording medium longer than a regular size, and fixes the toner image transferred to the long recording medium to the long recording medium by means of a fixing device.
2. Description of the Related Art
According to the above form of image forming apparatus that is configured as an electronic copying machine, a printer, a facsimile device or a complex machine thereof, an image can be formed on a long recording medium of, for example, 10 through 15 meters. A fixing device used in such an image forming apparatus has a fixing member, a pressure member pressure-contacted with the fixing member, first temperature detecting means for detecting the temperature of the fixing member, second temperature detecting means for detecting the temperature of the pressuring member, and heating means for heating the fixing member, wherein a long recording medium carrying a toner image is caused to pass through a nip portion formed between the fixing member and the pressure member, and heat and pressure are applied to a toner of the toner image on the long recording medium so that the toner image is fixed to the long recording medium.
In such a fixing device, by causing the long recording medium to pass between the fixing member and the pressure member, the heat of the fixing member is constantly lost to the long recording medium over a long period of time, whereby the temperature of the fixing member becomes lower than a temperature appropriate for fixing a toner image, while the long recording medium passes between the fixing member and the pressure member, causing a toner image fixation failure.
Therefore, it is necessary to use a fixing member having a large heat capacity in order to prevent the temperature of the fixing member from becoming lower than the temperature appropriate for fixing a toner image, when the long recording medium passes between the fixing member and the pressure member. However, the inevitable problem is that, if such a fixing member having a large capacity is used, the start-up time in which the temperature of the fixing member increases to the temperature appropriate for fixing a toner image becomes long when the start-up operation of the fixing device is performed.
Note that a general configuration of a fixing device used in an image forming apparatus is described in, for example, Japanese Unexamined Patent Application Publication No. 2002-184554, Japanese Unexamined Patent Application Publication No. 2005-39873, Japanese Unexamined Patent Application Publication No. 2005-32558, and Japanese Unexamined Patent Application Publication No. 2005-18049.